1. Field of the Invention
The present invention relates generally to coverlay substrates typically applied to a circuitized electronic substrate and thereafter modified by photolithography or the like. More specifically, the coverlays of the present invention comprise a multilayer composite containing a polyimide (or precursor thereto) based adhesive layer and a polyimide (or precursor thereto) based support layer, where the two layers combine to provide improved coverlay performance, such as reduced (unwanted) curl when bonded to “large surface area” flexible circuits.
2. Discussion of the Related Art
U.S. Pat. No. 5,336,925 to Moss et al. teaches “positive-working” photosensitive polyamic acids and compositions derived therefrom. Such compositions, when used as a circuit coverlay material, can exhibit undue curl of the circuit after bonding and curing, particularly for “large surface area” flexible circuits that are becoming increasingly prevalent in the industry.